A need exists for communicating data in a wellbore at rates far exceeding the capabilities of current wellbore telemetry systems. As one example, it would be very desirable to permanently install a large number of geophones in a wellbore and transmit data from the geophones simultaneously to a remote location, such as the earth's surface.
In this example, a telemetry data rate of about 30 Mbps might be required. Unfortunately, conventional wireline logging telemetry systems are capable of only about 300 kbps, which is two orders of magnitude less than the desired data rate.
Furthermore, conventional wireline logging telemetry systems are not designed to transmit data from widely distributed data sources. Instead, the data sources used with wireline logging tools are typically closely arranged in a well. Transmission of data from widely distributed data sources, on the other hand, can cause delays in relative transmission times between the respective data sources, thereby altering the relationships between the transmitted data.
In the case of seismic data, it is important for evaluation of the data that the data from separate sensors measured at a particular time be transmitted in a manner which permits this time relationship to be preserved. One manner of furthering this goal is to transmit the data from separate sources simultaneously via the same transmission channel. However, transmission of data from separate sources via the same transmission channel presents other challenges, such as how to differentiate one source's data from another source's data.
One type of telemetry system used in other applications is known as DMT VDSL (Discreet Multi-Tone Very-high-data-rate Digital Subscriber Line). The DMT VDSL system includes modems developed for high speed point-to-point communication over a telephone local subscriber loop. These modems are being commercialized currently for high speed internet connections.
However, DMT VDSL modems are suitable for communication only between two discreet endpoints. They are not capable of communicating data simultaneously between multiple widely distributed nodes and a remote location.